System and method for non-contact optical-power measurement

ABSTRACT

The present invention provides methods and systems for measuring optical power that require neither alterations to the optical fiber nor physical contact with the optical fiber, the system including an optical fiber configured to propagate an optical signal, wherein the optical fiber includes a core and at least a first cladding layer, wherein a portion of the optical signal scatters out of the optical fiber along a length of the optical fiber to form scattered fiber light; a detector system configured to receive the scattered fiber light along the length of the optical fiber and to output a detection signal based on the received scattered fiber light; and a processor configured to receive the detection signal and to determine a power value of the optical signal based on the received detection signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority benefit, under 35 U.S.C. §119(e), ofU.S. Provisional Patent Application No. 61/978,736, filed Apr. 11, 2014by Stephen J. Guimond, titled “SYSTEM AND METHOD FOR NON-CONTACTOPTICAL-POWER MEASUREMENT,” which is incorporated herein by reference inits entirety.

This application is related to:

U.S. Pat. No. 7,391,561 that issued Jun. 24, 2008 to Fabio Di Teodoro etal., titled “FIBER- OR ROD-BASED OPTICAL SOURCE FEATURING A LARGE-CORE,RARE-EARTH-DOPED PHOTONIC-CRYSTAL DEVICE FOR GENERATION OF HIGH-POWERPULSED RADIATION AND METHOD”;U.S. Pat. No. 7,570,856 that issued Aug. 4, 2009 to John D. Minelly etal., titled “APPARATUS AND METHOD FOR AN ERBIUM-DOPED FIBER FOR HIGHPEAK-POWER APPLICATIONS”;U.S. Pat. No. 7,768,700 that issued Aug. 3, 2010 to Matthias P.Savage-Leuchs, titled “METHOD AND APPARATUS FOR OPTICAL GAIN FIBERHAVING SEGMENTS OF DIFFERING CORE SIZES”;U.S. Pat. No. 7,876,803 that issued Jan. 25, 2011 to Fabio Di Teodoro etal., titled “HIGH-POWER, PULSED RING FIBER OSCILLATOR AND METHOD”;U.S. Pat. No. 7,876,498 that issued Jan. 25, 2011 to Eric C. Honea etal., titled “PULSE-ENERGY-STABILIZATION APPROACH ANDFIRST-PULSE-SUPPRESSION METHOD USING FIBER AMPLIFIER”;U.S. Pat. No. 7,924,500 that issued Apr. 12, 2011 to John D. Minelly,titled “MICRO-STRUCTURED FIBER PROFILES FOR MITIGATION OF BEND-LOSSAND/OR MODE DISTORTION IN LMA FIBER AMPLIFIERS, INCLUDING DUAL-COREEMBODIMENTS”;U.S. Pat. No. 8,934,509 that issued Jan. 13, 2015 to Matthias P.Savage-Leuchs et al., titled “Q-SWITCHED OSCILLATOR SEED-SOURCE FOR MOPALASER ILLUMINATOR METHOD AND APPARATUS”;U.S. Pat. No. 8,736,953 that issued May 27, 2014 to Matthias P.Savage-Leuchs, titled “HIGH-POWER LASER SYSTEM HAVING DELIVERY FIBERWITH NON-CIRCULAR CROSS SECTION FOR ISOLATION AGAINST BACK REFLECTIONS”;U.S. Pat. No. 8,830,568 that issued Sep. 9, 2014 to Matthias P.Savage-Leuchs et al., titled “HIGH BEAM QUALITY AND HIGH AVERAGE POWERFROM LARGE-CORE-SIZE OPTICAL-FIBER AMPLIFIERS”;U.S. Pat. No. 8,767,286 that issued Jul. 1, 2014 to Matthias P.Savage-Leuchs et al., titled “SIGNAL AND PUMP MODE-FIELD ADAPTOR FORDOUBLE-CLAD FIBERS AND ASSOCIATED METHOD”;U.S. Pat. No. 8,755,649 that issued Jun. 17, 2014 to Tolga Yilmaz etal., titled “IN-LINE FORWARD/BACKWARD FIBER-OPTIC SIGNAL ANALYZER”;U.S. Pat. No. 8,355,608 that issued Jan. 15, 2013 to Yongdan Hu, titled“METHOD AND APPARATUS FOR IN-LINE FIBER-CLADDING-LIGHT DISSIPATION”;U.S. Pat. No. 8,411,712 that issued Apr. 2, 2013 to Eric C. Honea etal., titled “BEAM DIAGNOSTICS AND FEEDBACK SYSTEM AND METHOD FORSPECTRALLY BEAM-COMBINED LASERS”;U.S. Pat. No. 8,503,840 that issued Aug. 6, 2013 to Yongdan Hu et al.,titled “OPTICAL-FIBER ARRAY METHOD AND APPARATUS”;U.S. patent application Ser. No. 14/086,744 by Eric C. Honea et al.,filed Nov. 21, 2013, titled “FIBER AMPLIFIER SYSTEM FOR SUPPRESSION OFMODAL INSTABILITIES AND METHOD” (Attorney Docket 5032.084US1);U.S. patent application Ser. No. 13/987,265 by Eric C. Honea et al.,filed Feb. 18, 2014, titled “APPARATUS AND METHOD FOR FIBER-LASEROUTPUT-BEAM SHAPING FOR SPECTRAL BEAM COMBINATION” (Attorney Docket5032.087US1);U.S. Provisional Patent Application 61/877,796 by Andrew Xing et al.filed Sep. 13, 2013, titled “APPARATUS AND METHOD FOR A DIAMONDSUBSTRATE FOR A MULTI-LAYERED DIELECTRIC DIFFRACTION GRATING” (AttorneyDocket 5032.085PV1);U.S. patent application Ser. No. 14/121,004 by Andrew Xing et al. filedSep. 15, 2014, titled “APPARATUS AND METHOD FOR A DIAMOND SUBSTRATE FORA MULTI-LAYERED DIELECTRIC DIFFRACTION GRATING” (Attorney Docket5032.085US1);U.S. Provisional Patent Application 61/854,277 by Yongdan Hu et al.filed Apr. 30, 2014, titled “SYSTEM AND METHOD FOR HIGH-POWER,HIGH-STRAYLIGHT-LOAD FIBER ARRAY” (Attorney Docket 5032.089PV1);U.S. patent application Ser. No. 13/999,557 by Gregory J. Whaley filedJun. 17, 2014, titled “METHOD AND APPARATUS FOR LOW-PROFILEFIBER-COUPLING TO PHOTONIC CHIPS” (Attorney Docket 5032.091US1);each of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to optical systems, and more particularlyto systems and methods for non-invasively measuring the power of opticalsignals propagating through optical systems (e.g., measuring the opticalpower propagating through an optical fiber without physically contactingthe optical fiber and/or without altering the optical fiber byside-polishing or inducing cladding propagation by bending the opticalfiber).

BACKGROUND OF THE INVENTION

A key parameter to monitor in any laser system is the power of theoptical signal produced by the laser system. Conventionaloptical-fiber-power-measurement systems generally fall into one of twocategories: (1) fiber-optic power measurement in which the fiber tip iscleaved or polished and inserted into a measurement head so that allpower is read and stopped at the measurement head (also referred toherein as “interruption” power measurement); and (2) fiber optic devicesfor which the optical fiber is side polished or otherwise incorporatedinto an “in-line” power monitor that has some non-zero insertion loss.

Interruption power monitors interrupt the optical train, rendering ituseless for in situ power measurement, monitoring, or fault detection.Examples of interruption power monitors include the Ophir PD300-IRGFiber Optic Power Meter Head by Ophir Optronics Solutions Ltd.(www.ophiropt.com/laser-measurement-instruments/new-products/pd300-r),and the Thorlabs S140C with S120-FC Fiber Adapter by Thorlabs Inc.(www.Thorlabs.com/newgrouppage9.cfm?objectgroup_id=3328&pn=S140C#6034).

Conventional in-line power monitors use taps that compromise fiberintegrity, risk optical damage at high power, and introduce insertionloss (e.g., conventional in-line power monitors alter the optical fiberin ways that risk damage in high-power applications, degrade opticalperformance, cause backscatter, and/or reduce power throughput).Examples of in-line power monitors include the EigenLight Series 500Inline Optical Power Monitor by EigenLight Corporation(www.eigenlight.com/products/portable-optical-power-monitors/series-500),and the FiberLogix Inline Power Monitor(www.fiberlogix.com/Passive/powermonitor.html). In-line power monitorsintroduce an insertion loss by tapping off some of the power in the coreto direct to an optical detector. In-line power monitors operate eitherby stripping off some optical power exploiting evanescent wave effectsor by means similar to optical couplers or splitters. Conventionalin-line power monitors are undesirable for efficiency and total powerreasons where an in-line device is to remain in place during fulloperation (e.g., when it is required in change-monitoring systems, powerfeedback systems, fault detection system, and the like). Someconventional in-line power monitors alter the fiber with a side polishor notch to redirect or probe the power propagating in the cladding.This introduces a weakness in the fiber both mechanically and in laserdamage threshold reduction. Alterations of the fiber surface andcladding are undesirable in high-power fiber laser systems. Conventionalin-line power monitors that use these tap and other principles ofoperation lack data for operation higher than 80 watts (W) and havedamage thresholds or max operating power specifications in the hundredsof milliwatts (mW) to a few 10's of watts range (e.g., approximately 50W). Conventional in-line power monitors and their possible faults alsointroduce safety risks should the system fail and fire or system damageoccur. Therefore, conventional in-line power monitors are unsuitable forsafely measuring optical power in high-power systems (e.g., about 1kilowatt or higher).

U.S. Patent Application Publication 2013/0087694 to Daniel J. Creeden etal. (hereinafter, “Creeden et al.”), titled “INTEGRATED PARAMETERMONITORING IN A FIBER LASER/AMPLIFIER,” published Apr. 11, 2013, and isincorporated herein by reference. Creeden et al. describe techniques formonitoring parameters in a high power fiber laser or amplifier systemwithout adding a tap coupler or increasing fiber length. In someembodiments, a cladding stripper is used to draw off a small percentageof light propagating in the cladding to an integrated signal parametermonitor. Parameters at one or more specific wavelengths (e.g., pumpsignal wavelength, signal/core signal wavelength, etc.) can bemonitored. In some such cases, filters can be used to allow forselective passing of signal wavelength to be monitored to acorresponding parameter monitor. The filters can be external or may beintegrated into a parameter monitor package that includes claddingstripper with integrated parameter monitor. Other parameters of interest(e.g., phase, wavelength) can also be monitored, in addition to, or asan alternative to power. Numerous configurations and variations will beapparent in light of this disclosure (e.g., system-on-chip).

U.S. Pat. No. 4,586,783 issued May 6, 1986 to Bruce D. Campbell et al.(hereinafter, “Campbell et al.”), titled “SIGNAL COUPLER FOR BUFFEREDOPTICAL FIBERS,” is incorporated herein by reference. Campbell et al.describe a signal coupler for buffered optical fibers that comprises asoft, transparent, polymeric rod against which the fiber is pressed by arigid “key” having regularly spaced protrusions which induce periodicmicrobending of the fiber. An optical signal passing down the fiber maybe coupled into the polymeric rod by the key pressing the fiber into therod, and the signal extracted from the end of the rod. A similar processmay be used to inject an optical signal into the fiber. The coupler maybe used either as a termination for a fiber or as part of anon-destructive tap. The induced attenuation and the intensity of theextracted signal may be varied by varying the pressure on the key.

U.S. Pat. No. 4,824,199 issued Apr. 25, 1989 to William D. Uken(hereinafter, “Uken”), titled “OPTICAL FIBER TAP UTILIZING REFLECTOR,”is incorporated herein by reference. Uken describes a tap forwithdrawing light from an intermediate portion of an optical fiber coreby passing light through a side of the optical fiber comprises anoptical coupler in contact with an outside surface of an optical fiberwhich is bent and disposed in a plane. A light reflector extendingtransverse to the plane deflects the withdrawn light towards the endsurface of a light element disposed completely outside the plane. Asimilar arrangement may be used to inject light to an intermediateportion of an optical fiber. The tap may be used as a read tap towithdraw light, or as a write tap to inject light in optical fibernetworks.

U.S. Pat. No. 6,424,663 issued Jul. 23, 2002 to Bernard Fidric et al.(hereinafter, “Fidric et al.”), titled “POWER MONITOR FOR FIBER GAINMEDIUM,” is incorporated herein by reference. Fidric et al. describe afiber optic gain system that has output power monitoring and controlusing the detected level of side light emitted through the cladding ofthe gain fiber. The fiber is wound on a spool that is provided with anopening adjacent to the fiber cladding. A photodetector is mounted tothe spool at an opposite side of the opening, and detects side lightthat is transmitted through the opening. An output signal from thephotodetector is indicative of the output power or the gain of thesystem, and may be used for monitoring and/or to adjust the powergenerated by a pumping source for the system. This allows feedbackcontrol of the system that helps to stabilize the output power or gain.A filtering element may also be used to exclude certain undesiredwavelengths from the side light being detected.

U.S. Pat. No. 6,744,948 issued Jun. 1, 2004 to Bo Pi et al.(hereinafter, “Pi et al.”), titled “FIBER TAP MONITOR BASED ONEVANESCENT COUPLING,” is incorporated herein by reference. Pi et al.describe fiber tap monitors formed on side-polished fiber coupling portsbased on evanescent coupling.

U.S. Pat. No. 7,116,870 issued Oct. 3, 2006 to Craig D. Poole(hereinafter, “Poole”), titled “BROADBAND FIBER OPTIC TAP,” isincorporated herein by reference. Poole describes a broadband opticalfiber tap for transferring optical energy out of an optical fiber havingan optical fiber with a primary and secondary microbends for the purposeof coupling optical energy into the higher-order modes of the fiber, anda reflecting surface formed in the cladding of the fiber and positionedat an angle so as to reflect, by total internal reflection, higher-ordermode energy away from the optical fiber. In the preferred embodiment,the two microbends are spaced apart by a distance approximately equal toone-half of the intermodal beat length for LP01 and LP11 modes of asingle-mode fiber.

U.S. Pat. No. 8,452,147 issued May 28, 2013 to Alexey V. Avdokhin et al.(hereinafter, “Avdokhin et al.”), titled “ASSEMBLY FOR MEASURING OPTICALSIGNAL POWER IN FIBER LASERS,” is incorporated herein by reference.Avdokhin et al. describe a fiber laser system configured with a powermeasuring assembly surrounding a splice between two fibers. The powermeasuring assembly is operative to maintain the splice at asubstantially constant splice temperature and shield the spliced fibersfrom external bending stresses so as to provide for power readings ofthe laser system at the splice independently from the influence ofmultiple variable external factors.

There is a need for an improved system and method for measuring thepower of optical signals propagating through an optical fiber.

SUMMARY OF THE INVENTION

In some embodiments, the present invention provides afiber-power-monitoring system that exploits the naturally occurringscattered energy that is a byproduct of optical-fiber propagation, andthus, in some embodiments, the present invention introduces noadditional throughput losses because it seeks to characterize only thepower lost to this inevitable scattering. In some embodiments, thepresent invention determines the optical power propagating through theoptical fiber without making alterations to the optical fiber (such asside polishing or introducing bends, stresses, splices or the like toinduce cladding propagation of some optical power). In some embodiments,the optical power is calculated from the naturally occurring corescattering so that physical contact is not required. In someembodiments, power measurement without physical contact increases thelaser damage threshold of the optical fiber under test. In someembodiments, the present invention provides a linear detector array andalgorithms operating on intensity-versus-position data in order todiscriminate scattering-per-unit-length from “hot spots,” cladding,buffer, or other non-uniform defects. In some embodiments, “hotspots” orspikes are eliminated prior to calculating an average or performing afunctional fit that is later mapped to a power calibration look-up tableor other functional mapping to power determinations. In someembodiments, the fiber-power-monitoring system of the present inventionis suitable for both high-power systems (e.g., about 1 kilowatt (kW) ormore) and systems that operate at power levels less than about 1 kW.

In some embodiments, the present invention provides a method formeasuring optical power that includes providing an optical-scatteringmedium (e.g., solid-state laser gain media such as Nd:YAG or passiveoptical materials such as fused silica, BK-7 glass, water, air, or thelike) configured to propagate an optical signal, wherein a portion ofthe optical signal scatters out of the optical-scattering medium along alength of the optical-scattering medium to form scattered light;imaging, at a first time period, the scattered light along the length ofthe optical-scattering medium and outputting a first image signal basedon the imaged scattered light; and determining a power value of theoptical signal based on the first image signal.

In some embodiments, the present invention includes a housing to holdthe fiber-power-monitoring system fixed with respect to the opticalfiber, imaging optics (such as a cylindrical lens and the like), alinear detector or arbitrary array of detectors, electronics forconverting the optical signal to analyzable data, algorithms for theanalysis of the data for pattern matching, data filtering, datarejection, intelligent selection of data, and the like, and theconversion of the analysis results to an optical power by means of afunction or calibration table.

In some embodiments, the present invention includes a variety of opticalcomponents and systems in the imaging train to assist in signaldiscrimination from noise, and remove bias from systematic errorsources. For example, in some embodiments, optical imaging componentsinclude polarization filters to discriminate scattered light from othersources. In some embodiments, optical imaging components includewavelength filters to discriminate signal from other background sources.In some embodiments, optical imaging components include neutral densityfilters to extend detector range and linearity. In some embodiments,optical imaging components include some combination of two or more ofthe above components.

In some embodiments, the present invention includes “upstream”fiber-treatment components that assist in improving calibrationrepeatability and accuracy. For example, in some embodiments, thepresent invention includes fiber loops on mandrels for stripping outcladding-mode power that might have been introduced by upstream fiberdefects and thus bias results idiosyncratically to local defects ratherthan overall fiber characterization. In some embodiments, the presentinvention includes cladding dumps formed by running fiber throughchannels of index matching fluids (with or without optional stripping ofbuffer or other layers as required for the particular fiber under test).

In some embodiments, the present invention provides imaging withoutcontacting the optical fiber to measure the optical power of an opticalsignal propagating in the optical fiber. In some embodiments, thepresent invention uses “naturally occurring” core-scattering whichrequires no additional signal boosts with bends, notches, or taps. Insome embodiments, the present invention exploits rejection algorithms tointelligently reject optical power outlier data points that correlate tofiber defects rather than true optical power. In some embodiments, thepresent invention exploits polarization properties ofpolarization-maintaining fibers and directionality of Rayleighscattering, coupled with lock-in detection & polarization modulation, todiscriminate core photons specifically.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a schematic diagram of a system 101 for measuring the opticalpower in an optical fiber 105.

FIG. 1B is a graph 102 depicting a linear-array image of fiber powerobtained by detector 140.

FIG. 1C is a block diagram of an algorithm 103 for calculating theoptical power in optical fiber 105.

FIG. 2 is a schematic diagram of a system 201 for measuring the opticalpower in optical fiber 105.

FIG. 3 is a schematic diagram of a system 301 for measuring the opticalpower in an optical fiber 305.

FIG. 4A is a schematic diagram of images 401 generated by a linear-arraydetector according to one embodiment of the present invention.

FIG. 4B is a graph 402 depicting a linear-array profile of fiber powerthat is generated based on one of the images 401 of FIG. 4A.

FIG. 4C is a graph 403 depicting the measured output power that isdetermined based, at least in part, on graph 402 of FIG. 4B.

FIG. 5A is a schematic diagram of a system 501 for measuring the opticalpower in an optical fiber.

FIG. 5B is a schematic diagram of images 503 generated by detector 540of FIG. 5A.

FIG. 5C is a schematic diagram of a system 504 for measuring the opticalpower in an optical fiber.

FIG. 6 is an overview diagram of a hardware- and operating-environment(or system) 601 that is used in conjunction with embodiments of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Although the following detailed description contains many specifics forthe purpose of illustration, a person of ordinary skill in the art willappreciate that many variations and alterations to the following detailsare within the scope of the invention. Specific examples are used toillustrate particular embodiments; however, the invention described inthe claims is not intended to be limited to only these examples, butrather includes the full scope of the attached claims. Accordingly, thefollowing preferred embodiments of the invention are set forth withoutany loss of generality to, and without imposing limitations upon theclaimed invention. Further, in the following detailed description of thepreferred embodiments, reference is made to the accompanying drawingsthat form a part hereof, and in which are shown by way of illustrationspecific embodiments in which the invention may be practiced. It isunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the present invention.The embodiments shown in the Figures and described here may includefeatures that are not included in all specific embodiments. A particularembodiment may include only a subset of all of the features described,or a particular embodiment may include all of the features described.

The leading digit(s) of reference numbers appearing in the Figuresgenerally corresponds to the Figure number in which that component isfirst introduced, such that the same reference number is used throughoutto refer to an identical component which appears in multiple Figures.Signals and connections may be referred to by the same reference numberor label, and the actual meaning will be clear from its use in thecontext of the description.

As used herein, “insertion loss” refers to the loss of signal powerresulting from the insertion of a device in an optical fiber.

FIG. 1A is a schematic diagram of a system 101 for measuring the opticalpower in an optical fiber 105. In some embodiments, system 101 measuresthe optical power of light 98 that is scattered by the core of opticalfiber 105 as it propagates through the core (e.g., in some embodiments,light 98 is light that is scattered via Rayleigh scattering). Sincesystem 101 measures naturally occurring scattered light 98, system 101,in some embodiments, provides optical power measurement withoutphysically altering and/or contacting optical fiber 105 such that thereis minimal or no insertion loss. In some embodiments, optical fiber 105includes a first cladding layer that surrounds the core and a secondcladding layer that surrounds the first cladding layer, wherein thefirst cladding layer has a lower index of refraction than that of thecore, and wherein the second cladding layer has a lower index ofrefraction than that of the first cladding layer. In some embodiments,system 101 includes imaging optics 120, secondary optics 130, a detector140, and a dark background 150. In some embodiments, system 101 furtherincludes a housing 160 that contains imaging optics 120, secondaryoptics 130, detector 140, and background 150, and is configured to holdsystem 101 fixed with respect to optical fiber 105 (in some embodiments,system 101 is fixed with respect to optical fiber 105 without the use ofhousing 160). In some embodiments, at least a portion of optical fiber105 is held in a fixed position by a spiral-mandrel assembly such asdescribed in U.S. patent application Ser. No. 14/086,744, which isincorporated herein by reference. In some embodiments, system 101includes a processor/controller 170 (e.g., a computer system) that isoperatively coupled to detector 140 via connection 175. In someembodiments, connection 175 is a wired connection. In other embodiments,connection 175 is a wireless connection. In some embodiments,processor/controller 170 is configured to process the data detected bydetector 140 and output a measured-optical-power value.

In some embodiments, imaging optics 120 includes a lens. In someembodiments, imaging optics 120 includes an imaging fiber that isoperatively coupled to detector 140. In some embodiments, secondaryoptics 130 assists with signal discrimination and noise/systemic errorfiltering. In some such embodiments, secondary optics 130 includes apolarization filter. In other such embodiments, secondary optics 130includes a wavelength filter configured to separate pump light fromsignal light. In other such embodiments, secondary optics 130 includesmodulation optics such as a photo-elastic modulator or liquid-crystalvariable retarder device that is configured to exploit lock-in detectionin order to distinguish core light from cladding light. In other suchembodiments, secondary optics 130 includes a neutral density filterconfigured to extend the range of detector 140 and configured to extendlinearity. In still other such embodiments, secondary optics 130includes a combination of two or more of the previously describedcomponents. In some embodiments, fiber 105 is oriented with respect toits core in order to optimize the degree of polarization of scatteredlight 98.

In some embodiments, detector 140 is a linear-array detector thatdetects light 98 across a length of optical fiber 105 in order to rejectdefects (e.g., hotspots 106) that may bias single-pixel measurements.For example, in some such embodiments, detector 140 is a complementarymetal-oxide-semiconductor (CMOS) linear image sensor such as provided byHamamatsu Photonics K.K.(www.hamamatsu.com/us/en/product/alpha/C/4119/index.html). In someembodiments, the Hamamatsu-CMOS-linear-image family of sensors detectslight in a range of 200 to 1000 nanometers (nm) and varies in pixelcount from 64 to 4098 pixels. In some embodiments, detector 140 is alinear-array detector such as the Indium-Gallium-Arsenide (InGaAs)p-type intrinsic n-type (PIN) photodiode array provided by HamamatsuPhotonics K.K.(www.hamamatsu.com/us/en/product/alpha/114107/index.html). In someembodiments, the Hamamatsu InGaAs-PIN-photodiode-array family of sensorsdetects light in a range of 700 to 1700 nm and varies in pixel countfrom 16 to 46 pixels. In some embodiments, detector 140 is amachine-vision camera such as the EO-0413M Monochrome USB 3.0 Cameraprovided by Edmunds Optics, Inc.(www.edmundoptics.com/imaging/cameras/usb-cameras/eo-usb-3-0-cmos-machine-vision-cameras/86-752).In some embodiments, detector 140 is a two-dimensional-array detector(also referred to herein as an M-by-N detector). In some embodiments,detector 140 is any other suitable imaging device (e.g., in someembodiments, detector 140 is any imaging device whose sensitivity isappropriate for the wavelength range or power range of interest). Insome embodiments, detector 140 is any other suitable light-detectiondevice (e.g., in some embodiments, detector 140 is any detector whosesensitivity is appropriate for the wavelength range or power range ofinterest).

In some embodiments, imaging and/or light-detection data obtained bydetector 140 is used with algorithms operating on anintensity-versus-position data in order to discriminatescattering-per-unit-length from hotspots 106, cladding, buffer, or othernon-uniform defects. In some embodiments, hotspots or spikes 106 areeliminated prior to calculating an average or performing a functionalfit that is later mapped to a power calibration look-up table or otherfunctional mapping to power determinations.

In some embodiments, system 101 is suitable for measuring optical powerin optical fiber that is in the high-power range (e.g., in someembodiments, at least one kilowatt (1 kW)) without risking laser damage.In some embodiments, system 101 provides optical power measurementswithout introducing insertion loss. In some embodiments, system 101provides optical power measurements without making physical contact withfiber 105 (or at least without making physical contact with the portionof optical fiber 105 being measured) in order to prevent laser damage.In some embodiments, system 101 provides power-change detection tofacilitate safety interlock or failsafe shutdown. In some embodiments,system 101 facilitates various closed-loop power response operations(e.g., closed loop constant power maintenance). In some embodiments,system 101 requires no splicing to optical fiber 105. In someembodiments, system 101 is movable to optimize system configuration. Insome embodiments, system 101 is removable should the user be interestedin using it only as a diagnostic or factory-set instrument. In someembodiments, system 101 remains in situ in order to monitor power duringoperation. In some embodiments, system 101 provides power calibrationfor a family of fibers.

FIG. 1B is a graph 102 depicting a linear-array image of fiber powerobtained by detector 140. In some embodiments, the linear-array dataprovided by detector 140 affords analysis by several means includingrejection of out-of-family hotspots or dark dropouts (e.g., hotspots106). In some embodiments, graph 102 is produced by processor/controller170.

FIG. 1C is a block diagram of an algorithm 103 for calculating theoptical power in optical fiber 105. In some embodiments, algorithm 103allows hot spots 106, which appear as “spikes” in the intensity versusposition data of FIG. 1B, to be filtered out in order to remove biasfrom the final calculation of power. In some embodiments, algorithm 103can be performed due to the inclusion of linear or two-dimensional arraydetectors (e.g., a linear-array detector such as described for detector140). In some embodiments, measuring power using a linear-array detectorwith algorithm 103 improves upon the power measurement of a single-pixeldetector (e.g., detector 240 of FIG. 2) because a single-pixel detectorwould likely be mislead by hot spots 106.

In some embodiments, at block 191 a detector (e.g., detector 140 of FIG.1A) captures an image of a length of optical fiber 105 (e.g., in someembodiments, the captured image shows intensity versus position alongthe length of fiber 105). In some embodiments, detector 140 sends dataregarding the captured image to a processor (e.g., processor/controller170 of FIG. 1A or system 601 of FIG. 6), which performs blocks 192-198.In some embodiments, at block 192, the background level in the imagedata is subtracted. In some embodiments, at block 193, the dataoutputted by block 192 is then divided by response versus position (alsoknown as “flat-field”). In some embodiments, at block 194, a FourierTransform is performed on the data outputted by block 193, and at block195, the resultant from block 194 is multiplied by a low-pass filter. Insome embodiments, at block 196, an inverse Fourier Transform isperformed on the data outputted by block 195. In some embodiments, theoutput of block 196 is combined with information from a calibrationlookup-table or a functional fit (e.g., see 197 to generate thecalculated power of block 198. In some embodiments, the FourierTransform of block 194 and the low-pass filter of block 195 are replacedby smoothing operations which replace the value at any pixel with theaverage of itself and some quantity of its neighbors to reduce theeffects of hotspots. In some embodiments, the Fourier Transform of block194 and the low-pass filter of block 195 are replaced by statisticalrejection which discards pixel values higher than certain thresholds inorder to discard “hotspot” outlier data.

FIG. 2 is a schematic diagram of a system 201 for measuring the opticalpower in optical fiber 105. In some embodiments, system 201 issubstantially similar to system 101 except that system 201 includes asingle-pixel detector 240. For example, in some embodiments of system201, detector 240 is an Indium-Gallium-Arsenide (InGaAs) Photodiode suchas provided by Thorlabs Inc.(www.thorlabs.com/thorproduct.cfm?partnumber=FDGA05). In some suchembodiments, detector 240 is fast enough to perform roles as a changedetector or failure-shutdown detector. In some embodiments of system201, secondary optics 120 includes a wavelength filter. In someembodiments, system 201 provides power measurement for relative power orfault detection. In some embodiments, system 201 is inexpensive and“clips-on” to any position in fiber 105. In some embodiments, system 201is used in combination with lock-in detection and polarizationmodulation such as described in FIG. 3.

FIG. 3 is a schematic diagram of a system 301 for measuring the opticalpower in an optical fiber 305. In some embodiments, optical fiber 305 isa polarization-maintaining (PM) fiber (e.g., a “panda” style fiber) andhas a known polarization orientation 308 (e.g., a slow-axis alignedpolarization) that shows the direction of the electric field of thecore-propagated light signal. In some embodiments, fiber 305 includes afiber core 306 and “panda”-style PM fiber-stress members 307. In someembodiments, due to the operation of Rayleigh scattering, photonsscattered in the direction perpendicular to both the fiber-propagationdirection and the polarization-electric-field direction (i.e. scatteredlight 98) is higher in intensity and degree of polarization. In someembodiments, therefore, core-scattered photons are distinguished frombackground levels by analyzing and/or modulating scattered light 98. Insome embodiments, due to the operation of Rayleigh scattering, photonsscattered in the direction parallel to the electric field of thepolarization (i.e., scattered light 97) are fewer and have a lowerdegree of polarization. In some embodiments, the optical components ofsystem 301 are arranged, based on polarization orientation 308, to takeadvantage of the high amount of Rayleigh scatter and high degree ofpolarization associated with scattered light 98. In some embodiments,system 301 provides optical power measurement without physicallyaltering and/or contacting optical fiber 305 such that there is minimalor no insertion loss. In some embodiments, system 301 provides powercalibration for a family of fibers.

In some embodiments, system 301 includes collimating optics 310 andimaging optics 320 (e.g., in some embodiments, a collimating lens 310and an imaging lens 320). In some embodiments, the space betweencollimating optics 310 and imaging optics 320 is collimated space 317,which is an appropriate region for placing a single or compound opticalassembly including, for example, wavelengths filters, neutral-densityfilters, polarization modulators (e.g., polarization-modulator 315),polarization filters (e.g., polarizer 316), and/or the like.

In some embodiments, polarization modulator 315 includes aliquid-crystal (LC) modulator. In some embodiments, polarizationmodulator 315 includes a photoelastic modulator (PEM). In someembodiments, polarization modulator 315 is any other suitablepolarization modulator. In some embodiments, polarizer 316 is an activepolarizer. In other embodiments, polarizer 316 is a passive polarizer.In some embodiments, polarization modulator 315 and polarizer 316 areconfigured to modify the polarization or the intensity amplitude oflight 98. In some embodiments, the polarization modification provided bymodulator 315 and polarizer 316, along with lock-in detection algorithmsprovided by processor/controller 370 (e.g., in some embodiments,processor/controller 370 includes a lock-in amplifier), help to improvethe signal-to-noise ratio of light 98 such that greater core-lightdistinction in light 98 can be achieved.

In some embodiments, system 301 further includes secondary optics 330(e.g., in some embodiments, a wavelength filter) and a detector 340. Insome embodiments, imaging optics 320 images light 98 onto detector 340.In some embodiments, detector 340 includes a linear-array detector thatis aligned along the length of fiber 305. In some embodiments, detector340 is a two-dimensional-array detector. In some embodiments, detector340 is a single-pixel detector. In some embodiments, detector 340 is acamera. In some embodiments, detector 340 is a high bandwidth (BW)detector. In some embodiments, detector 340 is any other suitablelight-detection device. In some embodiments, detector 340 is operativelycoupled to processor/controller 370 via connection 375, andprocessor/controller 370 is also operatively coupled to polarizationmodulator 315 via connection 376. In some embodiments, connection 375and 376 are wired connections. In some embodiments, connections 375 and376 are wireless connections. In some embodiments, one of connections375 and 376 is wired and the other connection is wireless.

FIG. 4A is a schematic diagram of images 401 generated by an imagingcamera. In some embodiments, each image 401 represents a differentoptical power that is detected at different times along the same lengthof an optical fiber (e.g., in some embodiments, each image 401 isgenerated using system 101 of FIG. 1A, but with the optical signal setat different power values for each image).

FIG. 4B is a graph 402 depicting a linear-array profile of fiber powerthat is generated based on one of the images 401 of FIG. 4A. In someembodiments, the present invention provides software (executed by, forexample, processor/controller 170 of FIG. 1A or system 601 of FIG. 6)that identifies and rejects local discontinuities in the linear-arrayprofile along the length of the optical fiber (e.g., in someembodiments, graph 402 identifies peaks in the linear-array profile thatare to be rejected when calculating output power).

FIG. 4C is a graph 403 depicting the measured output power that isdetermined based, at least in part, on graph 402 of FIG. 4B. In someembodiments, graph 403 shows how a functional fit (e.g., a linear fit)is made between the values detected by an array detector of the presentinvention and measured output power. In some embodiments, this linearfit is improved by the rejecting or trimming of hot spots from the rawdata such as the peaks identified in graph 402 of FIG. 4B. In someembodiments, the data used for graph 402 and graph 403 was based on anon-contact imaging experiment using system 101 of FIG. 1A thatdemonstrated the calibration and linearity associated with the powermeasurement of the present invention. In some embodiments, onlymonotonic behavior is required for the calibration shown in graph 403.

FIG. 5A is a schematic diagram of a system 501 for measuring the opticalpower in an optical fiber. In some embodiments, system 501 includes anoptical-signal generator 502 (in some embodiments, generator 502 is a300-W laser). In some embodiments, optical-signal generator 502 iscoupled to a passive double-clad optical fiber 505 having a20-micron-diameter (20 μm) core and a 400-micron-diameter (400 μm) outercladding (also referred to herein as a 20/400 optical fiber). In someembodiments, passive fiber 505 is spliced to a 5-meter-long gain fiber506 at splice 595. In some embodiments, gain fiber 506 is a double-cladPLMA-YDF (polarization-maintaining-large-mode-areaytterbium-doped-fiber) 20/400 optical fiber such as provided by nLight,Leiki, Nufern, CorActive, or the like. In some embodiments, gain fiber506 is coupled to a pump dump 507 (e.g., in some embodiments, pump dump507 includes a stripped gain fiber and/or an index-matching fluid oradhesive). In some embodiments, pump dump 507 is coupled to a doped gainfiber 508 that runs between pump dump 507 and a second pump dump 509. Insome embodiments, gain fiber 508 has a length of about 1 meter (3.28feet).

In some embodiments, system 501 further includes a power-detectionmodule 580 that is coupled to gain fiber 508 and configured to detect apower of an optical signal propagating through gain fiber 508. In someembodiments, module 580 includes a wavelength filter-520 configured toseparate pump light from signal light, a black background 550, and adetector 540 configured to image or detect the light scattered from thecore of fiber 508. In some embodiments, detector 540 is a detector orcamera such as described above for detector 140 of FIG. 1A. In someembodiments, fiber 508 is spliced to a passive single-clad 20/400delivery fiber 510 at splice 596. In some embodiments, delivery fiber510 is coupled to a calibration power meter 585 configured to providecalibration of power-detection module 580 (in some such embodiments,power meter 585 is an Ophir PD300-IRG Fiber Optic Power Meter Head byOphir Optronics Solutions Ltd.(www.ophiropt.com/laser-measurement-instruments/new-products/pd300-r)).In some such embodiments, placing meter 585 downstream of pump dumps 507and 509 assures that cladding pump light is subtracted from the signallight when analyzing the power-detection data generated by module 580.In some embodiments, system 501 further includes polarization modulationand lock-in detection (e.g., such as provided by system 301 of FIG. 3)to further improve the signal-to-noise ratio of the data generated bymodule 580.

FIG. 5B is a schematic diagram of images 503 generated by detector 540of FIG. 5A. In some embodiments, each image 503 represents a differentoptical power that is detected at different times along the same lengthof fiber 508. In some embodiments, the high-power imaging illustrated byimages 503 is scalable with appropriately chosen gain and attenuationfilters such as provided by system 501 of FIG. 5A.

FIG. 5C is a schematic diagram of a system 504 for measuring the opticalpower in an optical fiber. In some embodiments, system 504 issubstantially similar to system 501 of FIG. 5A except that deliveryfiber 510 is cleaved or polished such that there is a free space beambetween the end of delivery fiber 510 and power meter 585. In some suchembodiments, system 504 further includes a camera 531 that is configuredto image the light beam that is outputted from fiber 510 as the lightbeam strikes power meter 585. In some embodiments, an optical attenuator530 (e.g., a neutral density filter, partially reflecting mirror, smokedglass, or the like) is used to control optical power levels at camera531. In some embodiments, the imaging provided by camera 531 is used tocenter the light beam on power meter 585.

In some embodiments, system 504 is further used to calibrate system 580(e.g., in some embodiments, system 504 is used to create a look-up tableof system 580 response versus actual power at power meter 585). In someembodiments, power meter 585 is traceably calibrated to widely acceptedoptical power and wavelength standards (e.g., a National Institute ofStandards and Technology (NIST) traceable calibration). In someembodiments, detector 540 is a linear-array detector such as shown anddescribed for some embodiments of FIG. 1A (in some such embodiments,detector 540 is the CMOS linear-image sensor provided by HamamatsuPhotonics K.K. described above). In some embodiments, camera 531 is aduplicate model of detector 540. In some such embodiments, powerreadings at power meter 585 are used to confirm that camera 531 and thusdetector 540 have sufficient dynamic range to be useful over the powerrange for the intended application of system 580. In some embodiments,the pixel counts generated by camera 531 from imaging the light beam onpower meter 585 are used to determine whether camera 531 has a monotonicresponse (e.g., the pixel counts never decrease as the values of theoptical power increase) over sufficient optical power range.

FIG. 6 is an overview diagram of a hardware- and operating-environment(or system) 601 that is used in conjunction with embodiments of theinvention. The description of FIG. 6 is intended to provide a brief,general description of suitable computer hardware and a suitablecomputing environment in conjunction with which the invention may beimplemented. In some embodiments, the invention is described in thegeneral context of computer-executable instructions (e.g., in someembodiments, these instructions are stored on non-transient storagemedia such as USB FLASH drives, floppy disks, CDROM, storage connectedto the internet, or the like, and are used for performing a method usedin some embodiments of the present invention), such as program modules,that are stored on computer-readable media and that are executed bysystem 601, such as a microprocessor residing in a controller likeprocessor/controller 170 of FIG. 1A. Generally, program modules includeroutines, programs, objects, components, data structures, and the like,that perform particular tasks or implement particular abstract datatypes.

Moreover, those skilled in the art will appreciate that the inventionmay be practiced with other computer system configurations, includinghand-held devices, multiprocessor systems, microprocessor-based orprogrammable consumer electronics, network personal computers (networkPCs), minicomputers, mainframe computers, and the like. The inventionmay also be practiced in distributed computer environments where tasksare performed by input-output remote processing devices that are linkedthrough a communications network. In a distributed computingenvironment, program modules may be located in both local and remotememory storage devices.

In some embodiments, system 601 includes a user-control console computer20 that is programmable and that has a wireless (or wired, opticalfiber, or other direct connection) transceiver 71 that allows wirelesscontrol of, and/or sensing from (i.e., reprogramming of the remotemicroprocessors, as well as receiving sensed signals and diagnosticinformation from power-meter components 680 (e.g., in some embodiments,components 680 include polarization modulator 315 and detector 340 ofFIG. 3).

In some embodiments, hardware and operating environment 601 isapplicable to system 101, system 201, system 301, system 501, and/orsystem 504 of FIGS. 1A, 2, 3, 5A, and 5C, respectively, as a wholeand/or any of the individual components shown in FIGS. 1A, 2, 3, 5A,and/or 5C. In some embodiments, application programs 36 stored on acomputer-readable storage device (e.g., optical disk 31 (CDROM, DVD,Blu-ray Disc™ (BD), or the like), magnetic or FLASH storage device 29(e.g., floppy disk, thumb drive, SDHC™ (Secure-Data High-Capacity)memory card or the like), and/or a storage device 50 connected to aremote computer 49 (e.g., in some embodiments, customer devices 320 ofFIG. 3) that connects to computer 20 across a local-area network 51 or awide-area network 52 such as the internet) contain instructions and/orcontrol structures (such as look-up tables, control parameters,databases and the like) that are processed and/or transmitted tocomponents 680 to control their operation by methods of the presentinvention described herein. In some embodiments, the applicationsprograms 36 are partially executed in the computer 20.

As shown in FIG. 6, in some embodiments, the hardware- andoperating-environment includes user-control console computer 20, or aserver 20, includes a processing unit 21, a system memory 22, and asystem bus 23 that operatively couples various system componentsincluding the system memory 22 to the processing unit 21. In someembodiments, there may be only one, or in other embodiments, there maybe more than one processing unit 21, such that the processor of computer20 comprises a single central-processing unit (CPU), or a plurality ofprocessing units, commonly referred to as a multi-processor orparallel-processing environment. In various embodiments, computer 20 maybe implemented using a conventional computer, a distributed computer, orany other type of computer including those embedded in cell phones,personal-data-assistant devices or other form factors. For example, insome embodiments, computer 20 is implemented as any suitable computingdevice such as a desktop computer or a network of such computers, alaptop computer (e.g., a Macbook®), a tablet computer (e.g., an iPad®),a music and/or video-player computer (e.g., an iPod Touch®), a cellphone computer (e.g., an iPhone®), a smart television (one that canstream video programming from the internet), a video-streaming device(e.g., a Roku® or an AppleTV®) that obtains content from the internetand outputs the content to a conventional high-definition TV), acomputer/MP3-player/CD-player/GPS/phone system in an automobile or othervehicle, or any other suitable personal-computing (PC) platform(although several Apple® products are listed as typical examples heresince most persons of skill in the art can identify the type of deviceby analogy to such Apple® products, the products of any othermanufacturer may be substituted).

The system bus 23 can be any of several types of bus structuresincluding a memory bus or memory controller, a peripheral bus, and alocal bus using any of a variety of bus architectures. The system memorycan also be referred to as simply the memory, and includes read-onlymemory (ROM) 24 and random-access memory (RAM) 25. A basic input/outputsystem (BIOS) 26, containing the basic routines that help to transferinformation between elements within the computer (or server) 20, such asduring start-up, may be stored in ROM 24. The computer 20 furtherincludes a hard disk drive 27 for reading from and writing to a magnetichard disk, a removable-media drive or FLASH controller 28 for readingfrom or writing to a removable magnetic floppy-disk or FLASH storagedevice 29, and an optical disk drive 30 for reading from or writing to aremovable optical disk 31 (such as a CDROM, DVD, Blu-ray Disc™ (BD) orother optical media).

The hard disk drive 27, magnetic disk drive 28, and optical disk drive30 couple with a hard disk drive interface 32, a magnetic disk driveinterface 33, and an optical disk drive interface 34, respectively. Thedrives and their associated computer-readable media providenon-volatile, non-ephemeral storage of computer-readable instructions,data structures, program modules and other data for the computer 20. Itshould be appreciated by those skilled in the art that any type ofcomputer-readable media which can store data that is accessible by acomputer, such as magnetic cassettes, FLASH memory cards, digital videodisks, Bernoulli cartridges, random-access memories (RAMs), read-onlymemories (ROMs), redundant arrays of independent disks (e.g., RAIDstorage devices) and the like, can be used in the exemplary operatingenvironment.

A plurality of program modules that implement the methods of the presentinvention (e.g., a functional fit or look-up table ofarray-detector-pixel values to measured throughput power) can be storedon the hard disk, magnetic or FLASH storage device 29, optical disk 31,ROM 24, or RAM 25, including an operating system 35, one or moreapplication programs 36, other program modules 37, and program data 38.A plug-in program containing a security transmission engine for thepresent invention can be resident on any one, or on a plurality of thesecomputer-readable media.

In some embodiments, a user enters commands into the computer 20 throughinput devices such as a keyboard 40, pointing device 42 or othersuitable devices. These input devices are often connected to theprocessing unit 21 through a serial port interface 46 that is coupled tothe system bus 23, but can be connected by other interfaces, such as aparallel port, game port, or a universal serial bus (USB); a monitor 47or other type of display device can also be connected to the system bus23 via an interface, such as a video adapter 48. The monitor 47 candisplay a graphical user interface for the audiologist and/or user. Inaddition to the monitor 47, computers typically include other peripheraloutput devices (not shown), such as speakers and printers.

In some embodiments, computer 20 operates in a networked environmentusing logical connections to one or more remote computers or servers,such as remote computer 49. These logical connections are achieved by acommunication device coupled to or a part of the computer 20; theinvention is not limited to a particular type of communications device.The remote computer 49 can be another computer, a server, a router, anetwork PC, a client, a peer device or other common network node, andtypically includes many or all of the elements described above relativeto the computer 20, although only memory storage device 50 andapplication programs 36 have been illustrated in FIG. 6. The logicalconnections depicted in FIG. 4 include local-area network (LAN) 51 andwide-area network (WAN) 52. Such networking environments are commonplacein office networks, enterprise-wide computer networks, intranets and theInternet, which are all types of networks.

When used in a local-area networking (LAN) environment, the computer 20is connected to the LAN 51 through a network interface, modem or adapter53, which is one type of communications device. When used in a wide-areanetworking (WAN) environment such as the internet, the computer 20typically includes an adaptor or modem 54 (a type of communicationsdevice), or any other type of communications device, e.g., a wirelesstransceiver, for establishing communications over the wide area network52, such as the internet. The modem 54, which may be internal orexternal, is connected to the system bus 23 via the serial portinterface 46. In a networked environment, program modules depictedrelative to the personal computer 20, or portions thereof, can be storedin the remote memory storage device 50 of remote computer (or server) 49and accessed over the internet or other communications means. Note thatthe transitory signals on the internet may move stored program code froma non-transitory storage medium at one location to a computer thatexecutes the code at another location by the signals on one or morenetworks. The program instructions and data structures obtained from anetwork or the internet are not “stored” on the network itself, but arestored in non-transitory storage media that may be connected to theinternet from time to time for access. It is appreciated that thenetwork connections shown are exemplary, and in some embodiments, othermeans of, and communications devices for, establishing a communicationslink between the computers may be used including hybrid fiber-coaxconnections, T1-T3 lines, DSL's, OC-3 and/or OC-12, TCP/IP, microwave,WAP (wireless application protocol), and all other electronic mediathrough standard switches, routers, outlets and power lines, as the sameare known and understood by one of ordinary skill in the art.

The hardware and operating environment in conjunction with whichembodiments of the invention may be practiced has been described. Thecomputer 20 in conjunction with which embodiments of the invention canbe practiced can be a conventional computer, a distributed computer, orany other type of computer; the invention is not so limited. Such acomputer 20 typically includes one or more processing units as itsprocessor, and a computer-readable medium such as a memory. The computer20 can also include a communications device such as a network adapter ora modem, so that it is able to communicatively couple to othercomputers, servers, or devices. In some embodiments, one or more partsof system 601 elicits and receives input from a user, and based on theinput, modifies, adjusts or executes one or more of the methods of thepresent invention as described herein.

In some embodiments, the present invention uses a cleaved fiber launchfor an interrupted power measurement system such as shown in FIG. 5C. Insome embodiments, system 504 includes an optical-power head 585 (e.g.,in some embodiments, the Ophir PD300-IRG Fiber Optic Power Meter Head byOphir Optronics Solutions Ltd.(www.ophiropt.com/laser-measurement-instruments/new-products/pd300-r))coupled to a cleaved fiber tip 510. In some embodiments, system 504 alsoincludes neutral-density (ND) filters 530 and a camera 531. In someembodiments, the present invention provides an apparatus for measuringoptical power that includes an optical fiber configured to propagate anoptical signal, wherein the optical fiber includes a core and at least afirst cladding layer, wherein a portion of the optical signal scattersout of the optical fiber along a length of the optical fiber to formscattered fiber light; a linear-array detector configured to receive thescattered fiber light along the length of the optical fiber and tooutput a detection signal based on the received scattered fiber light;and a processor configured to receive the detection signal and todetermine a power value of the optical signal based on the receiveddetection signal.

In some embodiments of the apparatus, the linear-array detector includesa plurality of imaging pixels arranged in a linear configuration alongthe length of the optical fiber. In some embodiments, the apparatusfurther includes imaging optics located in between the optical fiber andthe linear-array detector, wherein the imaging optics is configured todirect the scattered fiber light onto the linear-array detector. In someembodiments, the apparatus further includes imaging optics located inbetween the optical fiber and the linear-array detector, wherein theimaging optics is configured to direct the scattered fiber light ontothe linear-array detector, and wherein the imaging optics includes alens.

In some embodiments of the apparatus, the scattered fiber light includesscattered pump light, the apparatus further comprising a wavelengthfilter configured to filter out the scattered pump light from thescattered fiber light before it reaches the linear-array detector.

In some embodiments, the apparatus further includes a housing configuredto hold the linear-array detector fixed with respect to the opticalfiber. In some embodiments, the optical fiber is apolarization-maintaining (PM) fiber, wherein a majority of the scatteredfiber light scatters in a first direction from the PM fiber, wherein thelinear-array detector is oriented to detect the scattered fiber lightthat scatters in the first direction. In some embodiments, the opticalfiber is a polarization-maintaining (PM) fiber, wherein the processorincludes a lock-in detection module, the apparatus further comprising aphotoelastic modulator (or liquid-crystal device or the like)operatively coupled to the processor and configured to modulate thepolarization of the scattered fiber light, wherein the processorcontrols the photoelastic modulator (or liquid-crystal device or thelike) and the lock-in detection module in order to improve thesignal-to-noise ratio of the scattered fiber light. In some embodiments,the processor is further configured to eliminate hot spots associatedwith the scattered fiber light during the determination of the powervalue of the optical signal.

In some embodiments, the processor is further configured to eliminatehot spots associated with the scattered fiber light during thedetermination of the power value of the optical signal, wherein theprocessor is further configured to perform a functional fit (orcalibration table lookup) of the determined power value to the scatteredfiber light, and wherein the functional fit (or calibration tablelookup) is used to calculate the power value.

In some embodiments, the apparatus further includes a plurality of pumpdumps; and a calibration power meter operatively coupled to an outputend of the optical fiber, wherein the calibration power meter isconfigured to provide power calibration of the apparatus.

In some embodiments, the present invention provides a method formeasuring optical power that includes providing an optical fiberconfigured to propagate an optical signal, wherein the optical fiberincludes a core and at least a first cladding layer, wherein a portionof the optical signal scatters out of the optical fiber along a lengthof the optical fiber to form scattered fiber light; imaging, at a firsttime period, the scattered fiber light along the length of the opticalfiber and outputting a first image signal based on the imaged scatteredfiber light; and determining a power value of the optical signal basedon the image signal.

In some embodiments, the method further includes focusing the scatteredfiber light prior to the imaging of the scattered fiber light. In someembodiments, the method further includes wavelength filtering thescattered fiber light to separate the portion of the optical signal frompump light (or other background light (e.g., room light)). In someembodiments, the optical fiber is a polarization-maintaining (PM) fiber,wherein a majority of the scattered fiber light scatters in a firstdirection from the PM fiber, wherein the imaging of the scattered fiberlight includes imaging the scattered fiber light that scatters in thefirst direction. In some embodiments, the optical fiber is apolarization-maintaining (PM) fiber, the method further comprisingmodulating the polarization of the scattered fiber light prior to theimaging of the scattered fiber light. In some embodiments, thedetermining of the power value of the optical signal includeseliminating hot spots associated with the scattered fiber light.

In some embodiments, the determining of the power value of the opticalsignal includes: eliminating hot spots associated with the scatteredfiber light; performing a functional fit (or calibration table lookup)of the determined power value to the scattered fiber light; imaging, ata second time period, subsequent to the first time period, the scatteredfiber light along the length of the optical fiber and outputting asecond image signal and determining, using the functional fit (orcalibration table lookup), a power value of the optical signal based onthe second image signal.

In some embodiments, the method further includes dumping pump lightalong the length of the optical fiber; and calibrating the determiningof the power value of the optical signal. In some embodiments, themethod further includes shutting off generation of the optical signal ifthe determined power value is different than (e.g., above, below, and/orvaries over time in a way that indicates a need for action) apredetermined level. In some embodiments, the method further includesstripping out cladding-mode power from the optical fiber prior to theimaging of the scattered fiber light.

In some embodiments, the present invention provides an apparatus thatincludes an optical fiber configured to propagate an optical signal,wherein the optical fiber includes a core and at least a first claddinglayer, wherein a portion of the optical signal scatters out of theoptical fiber along a length of the optical fiber to form scatteredfiber light; means for imaging the scattered fiber light along thelength of the optical fiber and outputting an image signal based on theimaged scattered fiber light; and means for determining a power value ofthe optical signal based on the image signal.

In some embodiments, the present invention provides a method formeasuring optical power that includes providing an optical-scatteringmedium (e.g., solid-state laser gain media such as Nd:YAG or passiveoptical materials such as fused silica, BK-7 glass, water, air, or thelike) configured to propagate an optical signal, wherein a portion ofthe optical signal scatters out of the optical-scattering medium along alength of the optical-scattering medium to form scattered light;imaging, at a first time period, the scattered light along the length ofthe optical-scattering medium and outputting a first image signal basedon the imaged scattered light; and determining a power value of theoptical signal based on the first image signal.

In some embodiments, the present invention provides an apparatus formeasuring optical power that includes an optical fiber configured topropagate an optical signal, wherein the optical fiber includes a coreand at least a first cladding layer, wherein a portion of the opticalsignal scatters out of the optical fiber along a length of the opticalfiber to form scattered fiber light; a detector system configured toreceive the scattered fiber light along the length of the optical fiberand to output a detection signal based on the received scattered fiberlight; and a processor configured to receive the detection signal and todetermine a power value of the optical signal based on the receiveddetection signal.

In some embodiments of the apparatus, the first cladding layer has anindex of refraction, wherein the optical fiber further includes a secondcladding layer that surrounds the first cladding layer along the lengthof the optical fiber, and wherein the second cladding layer has a lowerindex of refraction than the index of refraction of the first claddinglayer such that pump light inserted into the first cladding layer iscontained within the first cladding layer along the length of theoptical fiber. In some embodiments, the detector system includes asingle-pixel detector.

In some embodiments of the apparatus, the detector system includes aplurality of light-sensing positions, wherein the plurality oflight-sensing positions each collect light from at least one differentlocation. In some such embodiments, the detector system includes aone-by-N linear-array detector, and wherein N is an integer larger thanone. In some such embodiments, the detector system includes an M-by-Ndetector, wherein M and N are each an integer larger than one. In someembodiments, the detector system includes a plurality of single-pixeldetectors.

In some embodiments of the apparatus, the scattered fiber light includesscattered pump light, the apparatus further including imaging opticslocated between the optical fiber and the detector system, wherein theimaging optics is configured to direct the scattered fiber light ontothe detector system; and a wavelength filter configured to filter outthe scattered pump light from the scattered fiber light before itreaches the detector system. In some embodiments, the optical fiber is apolarization-maintaining (PM) fiber, wherein a majority of the scatteredfiber light scatters in a first direction from the PM fiber, wherein thedetector system is oriented to detect the scattered fiber light thatscatters in the first direction. In some embodiments, the optical fiberis a polarization-maintaining (PM) fiber, wherein the processor includesa lock-in detection module, the apparatus further includes apolarization modulator unit operatively coupled to the processor andconfigured to modulate a polarization of the scattered fiber light,wherein the polarization modulator unit includes a polarizer, whereinthe processor controls the polarization modulator unit and the lock-indetection module in order to improve the signal-to-noise ratio of thescattered fiber light (e.g., in some embodiments, the lock-in detectionmodule improves the detection of light scattered from the core overlight scattered from any other part of the fiber). In some suchembodiments, the polarization modulator unit includes a photoelasticmodulator. In some such embodiments, the polarization modulator unitincludes a liquid-crystal (LC) modulator. In some embodiments, thepolarization modulator includes a variable retarder. In someembodiments, the polarization modulator is any other suitablepolarization modulating device.

In some embodiments of the apparatus, the processor is furtherconfigured to eliminate hot spots associated with the scattered fiberlight during the determination of the power value of the optical signal.In some embodiments, the apparatus further includes one or more pumpdumps; and a calibration power meter optically coupled to the opticalfiber, wherein the calibration power meter is configured to providepower calibration of the apparatus.

In some embodiments of the apparatus, the optical fiber further includesa second cladding layer that surrounds the first cladding layer alongthe length of the optical fiber. In some such embodiments, the secondcladding layer has a low index of refraction such that pump lightinserted into the first cladding layer is contained within the firstcladding layer along the length of the optical fiber.

In some embodiments of the apparatus, the detector system includes aplurality of light-sensing positions, wherein the plurality oflight-sensing positions each collect light from at least one differentlocation, wherein the detector system includes a one-by-N linear-arraydetector, and wherein N is an integer larger than one. In someembodiments, the detector system includes a plurality of light-sensingpositions, wherein the plurality of light-sensing positions each collectlight from at least one different location, wherein the detector systemincludes an M-by-N detector, wherein M and N are each an integer largerthan one. In some embodiments, the detector system includes a pluralityof light-sensing positions, wherein the plurality of light-sensingpositions each collect light from at least one different location, andwherein the detector system includes a single-pixel detector. In someembodiments, the detector system includes a single-pixel detector.

In some embodiments, the apparatus further includes imaging opticslocated between the optical fiber and the detector system, wherein theimaging optics is configured to direct the scattered fiber light ontothe detector system. In some embodiments, the scattered fiber lightincludes scattered pump light, the apparatus further comprising awavelength filter configured to filter out the scattered pump light fromthe scattered fiber light before it reaches the detector system.

In some embodiments, the apparatus further includes a housing configuredto hold the detector system fixed with respect to the optical fiber. Insome embodiments, the optical fiber is a polarization-maintaining (PM)fiber, wherein a majority of the scattered fiber light scatters in afirst direction from the PM fiber, wherein the detector system isoriented to detect the scattered fiber light that scatters in the firstdirection. In some embodiments, the optical fiber is apolarization-maintaining (PM) fiber, wherein the processor includes alock-in detection module, the apparatus further including a photoelasticmodulator unit operatively coupled to the processor and configured tomodulate a polarization of the scattered fiber light, wherein thephotoelastic modulator unit includes a polarizer, wherein the processorcontrols the photoelastic modulator unit and the lock-in detectionmodule in order to improve the signal-to-noise ratio of the scatteredfiber light. In some embodiments, the optical fiber is apolarization-maintaining (PM) fiber, wherein the processor includes alock-in detection module, the apparatus further including aliquid-crystal (LC) modulator unit operatively coupled to the processorand configured to modulate a polarization of the scattered fiber light,wherein the LC modulator unit includes a polarizer, wherein theprocessor controls the LC modulator unit and the lock-in detectionmodule in order to improve the signal-to-noise ratio of the scatteredfiber light.

In some embodiments of the apparatus, the processor is furtherconfigured to eliminate hot spots associated with the scattered fiberlight during the determination of the power value of the optical signal.In some embodiments, the processor is further configured to eliminatehot spots associated with the scattered fiber light during thedetermination of the power value of the optical signal, wherein theprocessor is further configured to perform a functional fit of thedetermined power value to the scattered fiber light. In someembodiments, the apparatus further includes a plurality of pump dumps;and a calibration power meter configured to be temporarily coupled to anoutput end of the optical fiber, wherein the calibration power meter isconfigured to provide power calibration of the apparatus. In someembodiments, the apparatus further includes a plurality of pump dumps;and a calibration power meter optically coupled to an output end of theoptical fiber such that free space is located between the output end ofthe optical fiber and the calibration power meter, wherein thecalibration power meter is configured to provide power calibration ofthe apparatus.

In some embodiments, the present invention provides a method formeasuring optical power that includes providing an optical fiberconfigured to propagate an optical signal, wherein the optical fiberincludes a core and at least a first cladding layer, wherein a portionof the optical signal scatters out of the optical fiber along a lengthof the optical fiber to form scattered fiber light; detecting, at afirst time period, the scattered fiber light along the length of theoptical fiber and outputting a first signal based on the imagedscattered fiber light; and determining a power value of the opticalsignal based on the first signal.

In some embodiments of the method, the detecting includes imaging thescattered fiber light along the length of the optical fiber. In someembodiments, the scattered fiber light includes scattered pump light,the method further including focusing the scattered fiber light prior tothe detecting of the scattered fiber light; and wavelength filtering thescattered fiber light to separate the portion of the optical signal frompump light.

In some embodiments of the method, the optical fiber is apolarization-maintaining (PM) fiber, wherein a majority of the scatteredfiber light scatters in a first direction from the PM fiber, and whereinthe detecting of the scattered fiber light includes detecting thescattered fiber light that scatters in the first direction by lock-indetection, the method further including modulating a polarization of thescattered fiber light prior to the detecting of the scattered fiberlight.

In some embodiments of the method, the determining of the power value ofthe optical signal includes eliminating hot spots associated with thescattered fiber light. In some embodiments, the determining of the powervalue of the optical signal includes eliminating hot spots associatedwith the scattered fiber light; performing a functional fit of thedetermined power value to the scattered fiber light; detecting, at asecond time period, subsequent to the first time period, the scatteredfiber light along the length of the optical fiber and outputting asecond image signal; and determining, using the functional fit, a powervalue of the optical signal based on the second image signal.

In some embodiments, the method further includes dumping pump lightalong the length of the optical fiber; and calibrating the determiningof the power value of the optical signal. In some embodiments, themethod further includes providing a detector system configured toperform the detecting; and fixing a position of the detector system withrespect to the optical fiber. In some embodiments, the determining ofthe power value of the optical signal includes detecting apower-versus-time profile of the optical signal. In some embodiments,the method further includes controlling the optical signal based atleast in part on the power-versus-time profile (e.g. in someembodiments, the power-versus-time profile is used as part of a feedbacksystem to the optical signal generator/controller such that theoptical-signal generator/controller uses the power-versus-time profileto maintain constant optical power, shut down power if the power signalmeets certain profile criteria, and/or the like).

In some embodiments of the method, the optical fiber further includes asecond cladding layer that surrounds the first cladding layer along thelength of the optical fiber. In some such embodiments, the secondcladding layer has a low index of refraction such that pump lightinserted into the first cladding layer is contained within the firstcladding layer along the length of the optical fiber.

In some embodiments of the method, the detecting includes imaging thescattered fiber light along the length of the optical fiber. In someembodiments, the method further includes focusing the scattered fiberlight prior to the detecting of the scattered fiber light. In someembodiments, the method further includes wavelength filtering thescattered fiber light to separate the portion of the optical signal frompump light. In some embodiments, the optical fiber is apolarization-maintaining (PM) fiber, wherein a majority of the scatteredfiber light scatters in a first direction from the PM fiber, and whereinthe detecting of the scattered fiber light includes detecting thescattered fiber light that scatters in the first direction. In someembodiments, the optical fiber is a polarization-maintaining (PM) fiber,the method further including modulating a polarization of the scatteredfiber light prior to the detecting of the scattered fiber light. In someembodiments, the determining of the power value of the optical signalincludes eliminating hot spots associated with the scattered fiberlight. In some embodiments, the determining of the power value of theoptical signal includes eliminating hot spots associated with thescattered fiber light; performing a functional fit of the determinedpower value to the scattered fiber light; detecting, at a second timeperiod, subsequent to the first time period, the scattered fiber lightalong the length of the optical fiber and outputting a second imagesignal; and determining, using the functional fit, a power value of theoptical signal based on the second image signal.

In some embodiments, the method further includes dumping pump lightalong the length of the optical fiber; and calibrating the determiningof the power value of the optical signal. In some embodiments, thedetermining of the power value includes monitoring the power value ofthe optical signal over a plurality of time periods including the firsttime period. In some embodiments, the method further includescontrolling generation of the optical signal (e.g., shutting offgeneration, maintaining generation rate, adjusting generation rate, andthe like) based at least in part on the monitored power value (in somesuch embodiments, the monitored power value is transmitted (in someembodiments, via a wired connection; in other embodiments, via awireless connection) to the optical signal generator/controller as partof a feedback system). In some embodiments, the monitoring includesdetecting a time-versus-power profile of the optical signal. In someembodiments, the method further includes adjusting a temperature of theoptical fiber based at least in part on the monitored power value. Insome embodiments, the method further includes stripping outcladding-mode power from the optical fiber prior to the detecting of thescattered fiber light.

In some embodiments, the present invention provides an apparatus thatincludes an optical fiber configured to propagate an optical signal,wherein the optical fiber includes a core and at least a first claddinglayer, wherein a portion of the optical signal scatters out of theoptical fiber along a length of the optical fiber to form scatteredfiber light; means for detecting the scattered fiber light along thelength of the optical fiber and outputting a signal based on the imagedscattered fiber light; and means for determining a power value of theoptical signal based on the image signal.

In some embodiments, the present invention provides a non-transitorycomputer-readable medium containing instructions stored thereon forcausing a suitably programmed information processor to execute a methodfor determining optical power in an optical fiber based on signalsreceived from a detector, wherein the optical fiber includes a core andat least a first cladding layer, wherein a portion of the optical signalscatters out of the optical fiber along a length of the optical fiber toform scattered fiber light, wherein the portion of the optical signalthat scatters out of the optical fiber is detected by the detector, andwherein the computer-readable medium includes: instructions forreceiving a first signal from the detector, wherein the first signal isbased on scattered light detected from along the length of the opticalfiber during a first time period; instructions for calculating a powervalue based on the first signal that represents scattered fiber light;and instructions for outputting the calculated power value of theoptical signal.

Some embodiments of the computer-readable medium include a table ofcalibration values used to calibrate the power signal.

Some embodiments of the computer-readable medium further includeinstructions for causing imaging of the scattered fiber light along thelength of the optical fiber. In some embodiments, the scattered fiberlight includes scattered pump light, the computer-readable mediumfurther including instructions for causing the focusing of the scatteredfiber light prior to the detecting of the scattered fiber light; andinstructions for causing wavelength filtering of the scattered fiberlight to separate the portion of the optical signal from pump light.

In some embodiments of the computer-readable medium, the optical fiberis a polarization-maintaining (PM) fiber, wherein a majority of thescattered fiber light scatters in a first direction from the PM fiber,and wherein the detecting of the scattered fiber light includesdetecting the scattered fiber light that scatters in the first directionby lock-in detection, the computer-readable medium further includinginstructions for modulating a polarization of the scattered fiber lightprior to the detecting of the scattered fiber light.

Some embodiments of the computer-readable medium further includeinstructions such that the determining of the power value of the opticalsignal includes eliminating hot spots associated with the scatteredfiber light. In some embodiments, the computer-readable medium furtherinclude instructions such that the determining of the power value of theoptical signal includes eliminating hot spots associated with thescattered fiber light; performing a functional fit of the determinedpower value to the scattered fiber light; detecting, at a second timeperiod, subsequent to the first time period, the scattered fiber lightalong the length of the optical fiber and outputting a second imagesignal; and determining, using the functional fit, a power value of theoptical signal based on the second image signal.

Some embodiments of the computer-readable medium further includeinstructions for causing dumping of pump light along the length of theoptical fiber; and calibrating the determining of the power value of theoptical signal. In some embodiments, a detector system configured toperform the detecting is provided; and a position of the detector systemis fixed with respect to the optical fiber. In some embodiments, thecomputer-readable medium further includes instructions such that thedetermining of the power value of the optical signal includes detectinga power-versus-time profile of the optical signal. In some embodiments,the computer-readable medium further include instructions forcontrolling the optical signal based at least in part on thepower-versus-time profile (e.g. in some embodiments, thepower-versus-time profile is used as part of a feedback system to theoptical signal generator/controller such that the optical-signalgenerator/controller uses the power-versus-time profile to maintainconstant optical power, shut down power if the power signal meetscertain profile criteria, and/or the like).

In some embodiments of the computer-readable medium, the optical fiberfurther includes a second cladding layer that surrounds the firstcladding layer along the length of the optical fiber. In some suchembodiments, the second cladding layer has a low index of refractionsuch that pump light inserted into the first cladding layer is containedwithin the first cladding layer along the length of the optical fiber.

Some embodiments of the computer-readable medium further includeinstructions such that the detecting includes imaging the scatteredfiber light along the length of the optical fiber. In some embodiments,the computer-readable medium further includes instructions for causingthe focusing of the scattered fiber light prior to the detecting of thescattered fiber light. In some embodiments, the computer-readable mediumfurther includes instructions for causing wavelength filtering of thescattered fiber light to separate the portion of the optical signal frompump light. In some embodiments, the optical fiber is apolarization-maintaining (PM) fiber, wherein a majority of the scatteredfiber light scatters in a first direction from the PM fiber, and whereinthe computer-readable medium further includes instructions such that thedetecting of the scattered fiber light includes detecting the scatteredfiber light that scatters in the first direction. In some embodiments,the optical fiber is a polarization-maintaining (PM) fiber, thecomputer-readable medium further including instructions for causing themodulating of a polarization of the scattered fiber light prior to thedetecting of the scattered fiber light. In some embodiments of thecomputer-readable medium, the determining of the power value of theoptical signal includes eliminating hot spots associated with thescattered fiber light. In some embodiments, the computer-readable mediumfurther includes instructions such that the determining of the powervalue of the optical signal includes eliminating hot spots associatedwith the scattered fiber light; performing a functional fit of thedetermined power value to the scattered fiber light; detecting, at asecond time period, subsequent to the first time period, the scatteredfiber light along the length of the optical fiber and outputting asecond image signal; and determining, using the functional fit, a powervalue of the optical signal based on the second image signal.

Some embodiments of the computer-readable medium further includeinstructions for causing dumping of pump light along the length of theoptical fiber; and for calibrating the determining of the power value ofthe optical signal. In some embodiments, the determining of the powervalue includes monitoring the power value of the optical signal over aplurality of time periods including the first time period. In someembodiments, the computer-readable medium further includes instructionsfor causing the controlling of the generation of the optical signal(e.g., shutting off generation, maintaining generation rate, adjustinggeneration rate, and the like) based at least in part on the monitoredpower value (in some such embodiments, the monitored power value istransmitted (in some embodiments, via a wired connection; in otherembodiments, via a wireless connection) to the optical signalgenerator/controller as part of a feedback system). In some embodiments,the monitoring includes detecting a time-versus-power profile of theoptical signal. In some embodiments, the computer-readable mediumfurther includes instructions for causing the adjusting of a temperatureof the optical fiber based at least in part on the monitored powervalue. In some embodiments, the computer-readable medium furtherincludes instructions for causing the stripping out of cladding-modepower from the optical fiber prior to the detecting of the scatteredfiber light.

It is specifically contemplated that the present invention includesembodiments having combinations and subcombinations of the variousembodiments and features that are individually described herein (i.e.,rather than listing every combinatorial of the elements, thisspecification includes descriptions of representative embodiments andcontemplates embodiments that include some of the features from oneembodiment combined with some of the features of another embodiment,including embodiments that include some of the features from oneembodiment combined with some of the features of embodiments describedin the patents and patent-application publications incorporated byreference in the present application). Further, some embodiments includefewer than all the components described as part of any one of theembodiments described herein.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Although numerous characteristics andadvantages of various embodiments as described herein have been setforth in the foregoing description, together with details of thestructure and function of various embodiments, many other embodimentsand changes to details will be apparent to those of skill in the artupon reviewing the above description. The scope of the invention shouldbe, therefore, determined with reference to the appended claims, alongwith the full scope of equivalents to which such claims are entitled. Inthe appended claims, the terms “including” and “in which” are used asthe plain-English equivalents of the respective terms “comprising” and“wherein,” respectively. Moreover, the terms “first,” “second,” and“third,” etc., are used merely as labels, and are not intended to imposenumerical requirements on their objects.

What is claimed is:
 1. An apparatus for measuring optical powercomprising: an optical fiber configured to propagate an optical signal,wherein the optical fiber includes a core and at least a first claddinglayer, wherein a portion of the optical signal scatters out of theoptical fiber along a length of the optical fiber to form scatteredfiber light; a detector system configured to receive the scattered fiberlight along the length of the optical fiber and to output a detectionsignal based on the received scattered fiber light; and a processorconfigured to receive the detection signal and to determine a powervalue of the optical signal based on the received detection signal. 2.The apparatus of claim 1, wherein the first cladding layer has an indexof refraction, wherein the optical fiber further includes a secondcladding layer that surrounds the first cladding layer along the lengthof the optical fiber, and wherein the second cladding layer has a lowerindex of refraction than the index of refraction of the first claddinglayer such that pump light inserted into the first cladding layer iscontained within the first cladding layer along the length of theoptical fiber.
 3. The apparatus of claim 1, wherein the detector systemincludes a plurality of light-sensing positions, and wherein theplurality of light-sensing positions each collect light from at leastone different location.
 4. The apparatus of claim 3, wherein thedetector system includes a one-by-N linear-array detector, and wherein Nis an integer larger than one.
 5. The apparatus of claim 1, wherein thedetector system includes a single-pixel detector.
 6. The apparatus ofclaim 1, wherein the scattered fiber light includes scattered pumplight, the apparatus further comprising: imaging optics located betweenthe optical fiber and the detector system, wherein the imaging optics isconfigured to direct the scattered fiber light onto the detector system;and a wavelength filter configured to filter out the scattered pumplight from the scattered fiber light before it reaches the detectorsystem.
 7. The apparatus of claim 1, wherein the optical fiber is apolarization-maintaining (PM) fiber, wherein a majority of the scatteredfiber light scatters in a first direction from the PM fiber, and whereinthe detector system is oriented to detect the scattered fiber light thatscatters in the first direction.
 8. The apparatus of claim 1, whereinthe optical fiber is a polarization-maintaining (PM) fiber, wherein theprocessor includes a lock-in detection module, the apparatus furthercomprising: a polarization modulator unit operatively coupled to theprocessor and configured to modulate a polarization of the scatteredfiber light, wherein the polarization modulator unit includes apolarizer, wherein the processor controls the polarization modulatorunit and the lock-in detection module in order to improve thesignal-to-noise ratio of the scattered fiber light.
 9. The apparatus ofclaim 1, wherein the processor is further configured to eliminate hotspots associated with the scattered fiber light during the determinationof the power value of the optical signal.
 10. The apparatus of claim 1,further comprising: a pump dump; and a calibration power meter opticallycoupled to the optical fiber, wherein the calibration power meter isconfigured to provide power calibration of the apparatus.
 11. A methodfor measuring optical power comprising: providing an optical fiberconfigured to propagate an optical signal, wherein the optical fiberincludes a core and at least a first cladding layer, wherein a portionof the optical signal scatters out of the optical fiber along a lengthof the optical fiber to form scattered fiber light; detecting, at afirst time period, the scattered fiber light along the length of theoptical fiber and outputting a first signal based on the imagedscattered fiber light; and determining a power value of the opticalsignal based on the first signal.
 12. The method of claim 11, whereinthe scattered fiber light includes scattered pump light, the methodfurther comprising: focusing the scattered fiber light prior to thedetecting of the scattered fiber light; and wavelength filtering thescattered fiber light to separate the portion of the optical signal frompump light.
 13. The method of claim 11, wherein the optical fiber is apolarization-maintaining (PM) fiber, wherein a majority of the scatteredfiber light scatters in a first direction from the PM fiber, and whereinthe detecting of the scattered fiber light includes detecting thescattered fiber light that scatters in the first direction by lock-indetection, the method further comprising: modulating a polarization ofthe scattered fiber light prior to the detecting of the scattered fiberlight.
 14. The method of claim 11, wherein the determining of the powervalue of the optical signal includes eliminating hot spots associatedwith the scattered fiber light.
 15. The method of claim 11, wherein thedetermining of the power value of the optical signal includes:eliminating hot spots associated with the scattered fiber light;performing a functional fit of the determined power value to thescattered fiber light; detecting, at a second time period, subsequent tothe first time period, the scattered fiber light along the length of theoptical fiber and outputting a second image signal; and determining,using the functional fit, a power value of the optical signal based onthe second image signal.
 16. The method of claim 11, further comprising:dumping pump light along the length of the optical fiber; andcalibrating the determining of the power value of the optical signal.17. The method of claim 11, further comprising: providing a detectorsystem configured to perform the detecting; and fixing a position of thedetector system with respect to the optical fiber.
 18. The method ofclaim 11, wherein the determining of the power value of the opticalsignal includes detecting a power-versus-time profile of the opticalsignal.
 19. The method of claim 18, further comprising controlling theoptical signal based at least in part on the power-versus-time profile.20. An apparatus comprising: an optical fiber configured to propagate anoptical signal, wherein the optical fiber includes a core and at least afirst cladding layer, wherein a portion of the optical signal scattersout of the optical fiber along a length of the optical fiber to formscattered fiber light; means for detecting the scattered fiber lightalong the length of the optical fiber and outputting a signal based onthe imaged scattered fiber light; and means for determining a powervalue of the optical signal based on the image signal.